This disclosure relates generally to liquid crystal writing/drawing devices, and in particular, to Cholesteric Liquid Crystal Displays (ChLCDs) used in such writing/drawing devices.
Toy products are currently on the market such as Doodle Sketch (newer version of Magna Doodle) and Etch-a-Sketch®, both produced by the Ohio Arts Company—that allow children and other users to draw images on the device and to erase these images. The Doodle Sketch requires a specialized stylus (attached by a tether to the device) using a magnetophoretic display. The basic Etch-a-Sketch uses a built in specialized stylus controlled by two knobs to remove aluminum powder from the inside surface of a glass screen. These toy products are bulky, and the toys require a specialized stylus attached to the device. These toys cannot allow the user to freely create multiple images with the natural feel of writing on paper in brilliant color with a single movement of a non-specialized stylus, including a fingernail.
Toys that are electronic writing and drawing devices offer the benefits of multiple uses, neatness (i.e., no cleanup of paint, broken crayons, ink stains or pencil shavings) and ruggedness. Consumers currently choose toys that are electronic devices for a wide variety of features and, until very recently, benefits related to handwriting and drawing by hand have not been a major factor. In addition, consumers seeking a toy that is a low cost, rugged device to provide to their children for entertainment—such as on long automobile trips—are often frustrated and overwhelmed by the cost, complexity and fragility of electronic devices. Many electronic devices can be easily damaged or mishandled by children in their exuberance of use, or require extensive preparation by responsible adults to limit inappropriate access by children using the device. Many toys that mimic the look of more expensive devices but without their features quickly bore the child user.
The market for toys that are low-cost, low-power electronic devices that capture and display writing and drawing by hand continues to grow and is increasingly competitive. Consumers desire rugged devices that are easy to use and capture the experience of handwriting similar to the feel of writing with a pen on paper. In a world that strives for sustainability of natural resources, consumers and manufacturers seek alternatives to paper and paper-based solutions for easily and inexpensively capturing hand-written or hand-drawn ideas, information and images. Consumers also want their electronic devices to capture and present text and images in vibrant, unique and colorful ways, to mimic the use of pens and paper of different colors, without the expense, mess and single-use of pen and paper. Device ruggedness and visual appeal are particularly important for toys to appeal to children and to consumers purchasing products for children for both education and entertainment purposes.
In 2010, the Boogie Board® pressure sensitive cholesteric liquid crystal writing tablet, also referred to as an eWriter, of Kent Displays Inc. appeared on the market in which a pointed stylus or the fingernail can be used to write or trace an image on the surface of the tablet as described in U.S. Pat. Nos. 6,104,448 and 9,116,379, both patents being incorporated herein by reference. In a cholesteric liquid crystal writing tablet, the liquid crystal is sandwiched between two substrates including interior electrode layers, that are spaced to a particular cell gap. The front substrate is flexible and the bottom substrate is either opaque or semitransparent. Within the cell gap is a bistable cholesteric liquid crystal layer which can exhibit two textures, an essentially transparent (focal conic) texture and a color reflective (planar) texture. The spacing of the cell gap is usually set by plastic or glass spacers that are either cylindrical or spherical in shape. The tablet is initialized by applying voltage pulses to the electrodes to electrically drive the cholesteric material to the focal conic state. When one presses on the top substrate with a pointed stylus or finger, the liquid crystal is locally displaced. Flow induced in the liquid crystal changes its optical texture from essentially transparent to a brilliant reflective color at the location of the stylus. The reflective color contrasts well with the opaque or semitransparent color below the liquid crystal layer. An image traced by the stylus or fingernail will remain on the tablet indefinitely without application of a voltage until erased. Erasure is accomplished by applying a voltage pulse to the electrodes that drives the cholesteric liquid crystal from its color reflective state back to its essentially transparent state.
The above described principle known as Mode B is disclosed in more detail in U.S. Pat. No. 6,104,448, which is incorporated herein by reference. Another mode of operation, Mode A, can be used for the erasure of a selected portion of the image as disclosed in U.S. Pat. No. 8,139,039, which is incorporated herein by reference, and is applicable to the pressure sensitive liquid crystal devices of the present disclosure. The mode of operation with a color reflective background is termed Mode A whereas the other mode with an essentially transparent background is termed Mode B. In Mode A the tablet is initialized by electrically driving the pressure sensitive liquid crystal device to the color reflective texture with a voltage pulse or pulses. Then with a continuous voltage applied to the electrodes of an appropriate value, one can write images by driving the cholesteric material to the substantially transparent texture with the pressure of a pointed stylus.
The commercial Boogie Board® eWriter, operated in Mode B, has the color black for the fixed opaque light absorbing background. The dark black background offers high contrast for the color reflective image written on the eWriter. As disclosed in U.S. Pat. No. 5,493,430, which is incorporated herein by reference, other opaque colors may also be used for the fixed background of a cholesteric liquid crystal eWriter. The color of the background additively mixes with the color reflected by the cholesteric liquid crystal to present a different color than that of the cholesteric liquid crystal. There may be multiple colors on the background and those colors may be patterned. As an example, the pattern could be lines offering a lined tablet for convenience in writing text similar to a ruled paper tablet as described in U.S. Patent Application Publication No. 2013/0314621, which is incorporated herein by reference.
Prior art FIG. 1 illustrates a top view of an eWriter in mode B. The prior art procedure of writing an image on the eWriter is to first erase all previous images by applying an erasing voltage to drive the entire cell initially to the focal conic texture. The value of the voltage or magnitude of a voltage pulse to do this is well known in the art of making cholesteric liquid crystal displays, e.g., U.S. Pat. Nos. 5,453,863 and 5,691,795, both patents which are incorporated herein by reference. Typically, when a black back layer is used the cholesteric liquid crystal initially in the focal conic state appears dark because the cholesteric liquid crystal is weakly scattering or substantially transparent and reveals the black back layer. The pressure from the stylus 280 on the writing surface of the eWriter, without further application of voltage, induces flow that causes the liquid crystal to reorient to the bright planar texture. The cholesteric liquid crystal in the planar state has a certain bright color and a reflectance value at the wavelength of peak reflectance. The liquid crystal of the viewing area can be erased when switched back to the focal conic texture by applying the erasing voltage.
FIGS. 2A and 2B illustrate a top and side view, respectively, of a Boogie Board® eWriter with a semitransparent back layer that enables articles or back patterns to be viewed through the eWriter which can enable tracing, writing and drawing on the eWriter over the article or back pattern. This is described in U.S. Pat. No. 9,116,379, entitled “Electronic Display with Semitransparent Back Layer,” which is incorporated herein by reference in its entirety. The semitransparent back layer or back pattern, affects the image reflected by the liquid crystal through additive and/or subtractive color mixing. Here the article is a hand below the eWriter and the user is tracing the hand on the eWriter.
Many current eWriters are constructed to have a handheld size (e.g., current Boogie Board® eWriters by Kent Displays shown in FIGS. 1, 2A and 2B). This device is designed to have a pressure sensitivity that enables producing suitable written lines much like writing or drawing with a pen on a piece of paper without registering the palm of the hand on the eWriter. A stylus can be used to apply the pressure that changes liquid crystal reflectance. The stylus typically does not contain ink.
FIG. 3 shows a side view of the Prior Art Boogie Board® eWriter 10 and how the display subassembly 400 is supported. A bezel 402 with pressure sensitive adhesive 404 located at the perimeter of the eWriter device adheres to the front of the display subassembly and case 406. The display subassembly 400 is fixed in position by being trapped between the bezels 402 and the case 406, and is held in place with PSA 404.
Dry erase whiteboards have a large format and can be hung on a wall for writing and drawing for viewing by many people at once. However, these devices require use of markers and a dry eraser, which is costly and messy. Erasing often leaves a marker residue or after-image that can be difficult to remove. In addition, it is difficult to save the image written on a dry erase whiteboard, other than taking a photograph of it, which is cumbersome.
Large format Smart Board writing devices exist,such as in classrooms, but are very expensive and have complicated electronics.
A display subassembly of a large-format cholesteric liquid crystal writing device, if left free-floating over a back surface of the device, will eventually sag and pull away from the back surface, creating an undesirable look and writing experience. Current liquid crystal writing devices on the market, may attach the back case of the device to a back layer of the display subassembly using adhesive. However, such writing devices suffer from undesirable line acuity or line sharpness which detracts from the quality of the device and writing experience.
There is a need for a better technology to allow consumers of all ages to easily and repeatedly write, draw and immediately/simultaneously display to share contrasting, vibrant multiple color text and images for creative, educational and therapeutic uses. The present disclosure is directed to an eWriter having enhanced line acuity with other desirable features and characteristics that are detailed in the subsequent Summary of the Disclosure, Detailed Description, the accompanying drawings and the appended claims.